This invention relates to a novel method for preparing starch sulfate esters. More particularly, this invention relates to a method for preparing starch sulfate esters in water by the reaction of selected N-alkylimidazole-N'-sulfonates with a starch base under specified reaction conditions.
The modification of starch by chemical derivatization is well known and documented in such sources as "Starch and Its Derivatives", by J. S. Radley (1968) Fourth Edition, published by Chapman and Hall, Ltd., London. More particularly, the prior art teaches the preparation of starch sulfate esters in water by the reaction of starch with organic sulfating agents (U.S. Pat. Nos. 2,786,833 and 2,967,178) and, more recently, with inorganic sulfating agents (copending Patent Application to M. Tessler, Ser. No. 660,911 filed Feb. 24, 1976). The use of organic sulfating agents of the prior art, and in particular trimethylaminesulfur trioxide complex, to produce starch sulfate esters results in the production of organic by-products (e.g. trimethylamine) which are very difficult to remove properly from the final starch ester.
It is accordingly an object of the present invention to provide an improved method for preparing starch sulfate esters in water using organic sulfating agents. A further object is to provide a method for preparing starch sulfate esters in water which results in the production of organic by-products which are readily removed from the final starch ester. These and other objects will be apparent from the following description.